Light-emitting device comprising led chip and method for manufacturing this device

ABSTRACT

A light emitting device includes a first patterned electrode  12  and a second patterned electrode  13  both of which are formed on a wiring board  11,  an LED chip  19  mounted on the second patterned electrode  13,  a metal wire  20  electrically connecting the LED chip  19  and the first patterned electrode  12  to each other, and a lens member  21  made of a transparent synthetic resin for packaging the LED chip  19  and the metal wire  20.  The first patterned electrode  12  is circular and formed with a cutout  14  at the center thereof. The second patterned electrode  13  is arranged in the cutout  14.  With this arrangement, the lens member  21  can be formed into a predetermined configuration, while the reflection of light by the patterned electrodes can be ensured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device including anLED chip mounted on e.g. a printed wiring board and packaged in a lensmember made of a synthetic resin, while also relating to a method ofmaking such a device.

2. Description of the Related Arts

A typical light emitting device of the above-described type includes apair of first patterned electrode and second patterned electrode formedon an upper surface of a wiring board. On the upper surface of thesecond patterned electrode is mounted an LED chip, which is electricallyconnected to the first patterned electrode by wire bonding using a thinmetal wire. A lens member made of a transparent synthetic resin isformed on the upper surface of the wiring board at the portion where theLED chip is mounted to package the LED chip and the metal wire.

FIGS. 10 and 11 show a structure disclosed in JP-A 4-28269 as a priorart device. Specifically, a second patterned electrode 2 of a metal filmis formed into a circular configuration on the upper surface of a wiringboard 1, and an LED chip is mounted at the center of the circle. Thecircular second patterned electrode 2 is formed with a cutout 4extending radially inward from the circumference of the circle towardthe LED chip 3. A first patterned electrode 5 of a metal film is formedon the upper surface of the wiring board 1 to extend radially outwardfrom a portion within the cutout 4. The inner end of the first patternedelectrode 5 is electrically connected to the LED chip 3 by wire bondingusing a thin metal wire 6. On the upper surface of the second patternedelectrode 2 is provided a lens member 7 formed by dropping anappropriate amount of transparent synthetic resin in a liquid state ontothe second patterned electrode for bulging the resin into ahemispherical configuration and then hardening the resin.

In the prior art structure, since the lens member 7 is provided on thesecond patterned electrode 2 in the form of a circular metal film, thecircular second patterned electrode 2 serves as a reflection film of thelight emitted from the LED chip 3, whereby the brightness of the emittedlight is enhanced.

However, the following problem is caused by the provision of the cutout4 extending from the circumference of the second patterned electrode 2toward the LED chip 3 and the provision of the first patterned electrode5 of the metal film in the cutout 4 to extend radially outward.

When the transparent synthetic resin for forming the lens member 7 isdropped, in a liquid state, onto the upper surface of the circularsecond patterned electrode 2, the transparent synthetic resin spreadsradially outward over the circular second patterned electrode 2 to reachthe outer circumference of the second patterned electrode 2 and bulgesinto a generally hemispherical configuration on the second patternedelectrode due to the surface tension. In this state, the synthetic resinis hardened to become the lens member 7.

However, since the outer circumference of the second patterned electrode2 is interrupted at the portion formed with the cutout 4, and the firstpatterned electrode 5 is provided at the cutout 4 to project outward,part of the transparent synthetic resin dropped in a liquid state ontothe second patterned electrode 2 spreads through the cutout 4, i.e.along the upper surface of the first patterned electrode 5 to projectoutward from the outer circumference of the second patterned electrode2.

As a result, the lens member 7 after the hardening does not become around circle corresponding to the configuration of the second patternedelectrode 2 as viewed in plan but becomes an irregular shape partiallyprojecting outward at the portion where the first patterned electrode 5is provided. Further, the configuration cannot be made generally uniformwith respect to a plurality of lens members 7, and the variation of theconfiguration of the lens members is large.

Conventionally, to solve the above problem, a dam ring 8 surrounding theLED chip 3 and the metal wire 6 is provided on the upper surface of thecircular second patterned electrode 2, as shown in FIG. 12. By droppingthe transparent synthetic resin in a liquid state into the dam ring 8,the lens member 7 having a predetermined configuration can be formed,and the variation of the lens configuration can be reduced.

However, the provision of the dam ring 8 on the circular secondpatterned electrode 2 increases the manufacturing cost, which may resultin the price increase. Further, the dam ring 8 blocks the light emittedfrom the LED chip 3 to reduce the amount of light.

It is, therefore, an object of the present invention to provide a lightemitting device capable of solving the above-described problems and toprovide a method of making such a device.

DISCLOSURE OF THE INVENTION

According to a first aspect of the present invention, which relates to alight emitting device structure, there is provided a light emittingdevice comprising: a first patterned electrode and a second patternedelectrode both of which are made of a metal film and provided on anobverse surface of a wiring board; an LED chip mounted on the secondpatterned electrode; a metal wire electrically connecting the LED chipand the first patterned electrode to each other; and a lens member madeof a transparent synthetic resin and provided on the obverse surface ofthe wiring board for packaging the LED chip and the metal wire. Thefirst patterned electrode is circular and has a central cutout, and thesecond patterned electrode is arranged in the cutout.

With such an arrangement, since the second patterned electrode isdisposed in the cutout formed at the center of the circular firstpatterned electrode, the circular first patterned electrode completelysurrounds the entire circumference of the second patterned electrode towhich the LED chip is mounted. The outer circumference of the firstpatterned electrode becomes a completely closed circle with nointerruption. Therefore, when an appropriate amount of transparentsynthetic resin in a liquid state is dropped onto the first patternedelectrode, the liquid transparent synthetic resin spreads radiallyoutward over the upper surface of the first patterned electrode to reachthe outer circumference of the first patterned electrode and bulges, dueto the surface tension, into a generally hemispherical configurationwithout spreading beyond the outer circumference of the first patternedelectrode. Therefore, unlike the prior art structure, projecting of thebulged transparent synthetic resin beyond the circumference of thecircle, which results in an irregular configuration of the lens member,can be reliably prevented.

Moreover, since both of the circular first patterned electrode and thesecond patterned electrode arranged in the cutout of the first patternedelectrode are made of a metal film, the light emitted from the LED chipcan be reflected away from the wiring board.

Therefore, according to the first aspect, the light emitted from the LEDchip can be reliably reflected toward the lens member by each of thepatterned electrodes. Further, the lens member can be formed into apredetermined configuration, and variation of the lens configuration canbe reduced. Moreover, unlike the prior art structure, a dam ring forsurrounding the lens member need not be provided, so that the brightnessof the light can be enhanced.

According to a second aspect of the present invention, which alsorelates to a light emitting device structure, there is provided a lightemitting device comprising: a first patterned electrode and a pluralityof second patterned electrodes, the first and second patternedelectrodes being made of a metal film and provided on an obverse surfaceof a wiring board; LED chips each mounted on a respective one of thesecond patterned electrodes; metal wires each electrically connecting arespective one of the LED chips and the first patterned electrode; and alens member made of a transparent synthetic resin and provided on theobverse surface of the wiring board for packaging the LED chips and themetal wires. The first patterned electrode is circular and has a centralcutout. The second patterned electrodes are arranged in the cutout whilebeing equally spaced from each other along the circumference of a circlewhich is generally concentric with the circle of the first patternedelectrode. The metal wires electrically connecting the LED chips mountedon the second patterned electrodes to the first patterned electrodeextend radially outward.

With such a structure, the metal wires for a plurality of LED chipsprovided in the single lens member extend radially outward. Therefore,the radially outward flow of the liquid transparent synthetic resindropped onto the first patterned electrode occurs generally in the samemanner at respective portions provided with the metal wires. As aresult, the liquid transparent synthetic resin reliably spreads tobecome a round circle. Therefore, the same advantages as described abovecan be provided with respect to a light emitting device provided with aplurality of LED chips.

In the first aspect and the second aspect, the wiring board has areverse surface formed with a power supply wiring pattern for electricalconnection to the first patterned electrode and the second patternedelectrode via a through-hole formed in the wiring board. With such astructure, the power supply for the first patterned electrode and thesecond patterned electrode can be performed by the power supply wiringpattern formed on the reverse surface of the wiring board, and theformation of the power supply wiring pattern on the reverse surface canbe performed easily.

In the second aspect, the cutout of the first patterned electrode mayhave a peripheral edge which includes an indentation entering betweenthe second patterned electrodes. With such an arrangement, the lightreflective surface comprising the first patterned electrode can beincreased by as much as the portions entering between the secondpatterned electrodes, whereby the brightness of the light can be furtherenhanced.

According to a third aspect of the present invention, which relates to amethod of making a light emitting device, a method is provided whichcomprises the steps of: forming, on a wiring board, a first patternedelectrode of a metal film into a circular configuration while forming acutout at the center of the first patterned electrode; forming a secondpatterned electrode of a metal film in the cutout; mounting an LED chipon the second patterned electrode; electrically connecting the LED chipand the first patterned electrode to each other via a metal wire; andforming a lens member by dropping transparent synthetic resin in aliquid state onto the first patterned electrode so that the transparentsynthetic resin bulges to cover the LED chip and the metal wire and thenhardening the synthetic resin.

With such a method, unlike the prior art technique, a light emittingdevice having the above-described advantages can be manufactured at lowcost without using a dam ring surrounding the lens member.

Other objects, features and advantages of the present invention willbecome clearer from the description of the embodiments given below withreference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a first embodiment of the presentinvention.

FIG. 2 is a sectional view taken along lines II-II in FIG. 1.

FIG. 3 is a plan view showing a second embodiment of the presentinvention.

FIG. 4 is a sectional view taken along lines IV-IV in FIG. 3.

FIG. 5 is a plan view showing a third embodiment of the presentinvention.

FIG. 6 is a sectional view taken along lines VI-VI in FIG. 5.

FIG. 7 is a perspective view showing a fourth embodiment of the presentinvention.

FIG. 8 is a plan view showing a principal portion of the fourthembodiment.

FIG. 9 is a sectional view taken along lines IX-IX in FIG. 8.

FIG. 10 is a plan view showing an example of prior art device.

FIG. 11 is a sectional view taken along lines XI-XI in FIG. 10.

FIG. 12 is a sectional view showing another example of prior art device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

FIGS. 1 and 2 show a first embodiment of the present invention. In thisembodiment, a single LED chip is utilized.

Designated by the reference sign 11 in these figures is a wiring boardmade of an insulating material such as glass-fiber-reinforced epoxyresin (glass fibers hardened with an epoxy resin). On the upper surfaceof the wiring board 11 are formed a first patterned electrode 12 and asecond patterned electrode 13, which are made of a metal film comprisinga copper foil and a gold plating layer formed thereon via an underlyingnickel plating layer, for example.

The first patterned electrode 12 is circular with a diameter D. Thefirst patterned electrode 12 has a cutout 14 at the center thereof. Thesecond patterned electrode 13 is circular with a smaller diameter d andarranged in the cutout 14 of the first patterned electrode 12 whilebeing spaced from the first patterned electrode 12 like an island.

On the lower surface of the wiring board 11 are formed a power supplywiring pattern 15 for the first patterned electrode 12, and a powersupply wiring pattern 16 for the second patterned electrode 13. Thewiring patterns 15 and 16 are electrically connected to the patternedelectrodes 12 and 13, respectively, via through holes 17 and 18penetrating the wiring board 11.

On the second patterned electrode 13, an LED chip 19 is mounted, by diebonding, at a portion corresponding to the center of the circle of thefirst patterned electrode 12. The LED chip 19 is electrically connectedto the first patterned electrode 12 by wire bonding using a thin metalwire 20.

An appropriate amount of transparent synthetic resin such as an epoxyresin in a liquid state is dropped onto the upper surface of the wiringboard 11 at the portion formed with the first patterned electrode 12(preferably at the general center of the first patterned electrode 12)by potting which is conventionally known.

The circular first patterned electrode 12 completely surrounds theentire circumference of the second patterned electrode 13 to which theLED chip 19 is mounted, and the outer circumference of the firstpatterned electrode is a completely closed circle with no interruption.Therefore, the transparent synthetic resin dropped thereon in a liquidstate spreads radially outward over the upper surface of the firstpatterned electrode 12 to reach the outer circumference of the firstpatterned electrode 12 and bulges, due to the surface tension, into agenerally hemispherical configuration without spreading beyond the outercircumference.

The liquid transparent synthetic resin bulged in the above manner isthen hardened by heating or ultraviolet irradiation, thereby providing agenerally hemispherical lens member 21 which packages the LED chip 19and the metal wire 20.

FIGS. 3 and 4 show a second embodiment of the present invention. In thesecond embodiment, two LED chips 19 a, 19 a′ for emitting light of thesame color or different colors are utilized.

Designated by the reference sign 11 a in these figures is a wiring boardmade of an insulating material. On the upper surface of the wiring board11 a are formed a first patterned electrode 12 a and two secondpatterned electrode 13 a, 13 a′, which are made of a metal filmsimilarly to those of the first embodiment.

The first patterned electrode 12 a is circular with a diameter D. Thefirst patterned electrode 12 a has a cutout 14 a at the center thereof.Each of the two second patterned electrodes 13 a, 13 a′ is circular witha smaller diameter d. The two second patterned electrodes 13 a, 13 a′are arranged in the cutout 14 a of the first patterned electrode 12 awhile being equally spaced, like islands, along the circumference of acircle s which is generally concentric with the circular first patternedelectrode 12 and has a radius r, as viewed in plan (FIG. 3).

On the lower surface of the wiring board 11 a are formed a power supplywiring pattern 15 a electrically connected to the first patternedelectrode 12 a via a through hole 17 a, a power supply wiring pattern 16a electrically connected to the second patterned electrode 13 a via athrough hole 18 a, and a power supply wiring pattern 16 a′ electricallyconnected to the second patterned electrode 13 a′ via a through hole 18a′.

On the second patterned electrodes 13 a and 13 a′ are mounted LED chips19 a and 19 a′, respectively at the generally center thereof, by diebonding. The LED chips 19 a, 19 a′ are electrically connected to thefirst patterned electrode 12 a by wire bonding using thin metal wires 20a, 20 a′.

The metal wires 20 a, 20 a′ are so arranged as to extend in oppositedirections from the LED chip 19 a, 19 a′ as viewed in plan (FIG. 3),i.e., extend radially outward.

Similarly to the first embodiment, an appropriate amount of transparentsynthetic resin in a liquid state is dropped onto the upper surface ofthe wiring board 11 a at the portion formed with the first patternedelectrode 12 a (preferably at the general center of the first patternedelectrode 12 a) to cause the resin to bulge into a hemisphericalconfiguration, and then the bulged resin is hardened. As a result, ahemispherical lens member 21 a is provided which packages the LED chips19 a, 19 a′ and the metal wires 20 a, 20 a′.

As noted above, the metal wires 20 a, 20 a′ for the LED chips 19 a, 19a′ extend in opposite directions from each other, i.e., extend radiallyoutward. Therefore, the radially outward flow of the liquid transparentsynthetic resin dropped onto the first patterned electrode 12 a occursgenerally in the same manner at respective portions provided with themetal wires 20 a and 20 a′. As a result, the liquid transparentsynthetic resin reliably spreads to become a round circle, as viewed inplan (FIG. 3).

The peripheral edge of the cutout 14 a of the first patterned electrode12 a includes indentations 12 a′, 12 a″ entering between the secondpatterned electrodes 13 a and 13 a′. By the provision of theindentations 12 a′ and 12 a″, the light reflective surface comprisingthe first patterned electrode 12 a can be increased by as much as theportions entering between the second patterned electrodes 13 a and 13a′.

FIGS. 5 and 6 show a third embodiment of the present invention.

In the third embodiment, three LED chips, i.e., an LED chip 19 b foremitting red light, an LED chip 19 b′ for emitting green light, and anLED chip 19 b″ for emitting blue light are utilized.

Designated by the reference sign 11 b in these figures is a wiring boardmade of an insulating material. On the upper surface of the wiring board11 b, a first patterned electrode 12 b and three second patternedelectrode 13 b, 13 b′, 13 b″ are formed, which are made of a metal filmsimilarly to those of the first and the second embodiments.

The first patterned electrode 12 b is circular with a diameter D. Thefirst patterned electrode 12 b has a cutout 14 b at the center thereof.Each of the three second patterned electrodes 13 b, 13 b′, 13 b″ iscircular with a smaller diameter d. The three second patternedelectrodes 13 b, 13 b′, 13 b″ are arranged, like islands, in the cutout14 b of the first patterned electrode 12 b while being equally spacedfrom each other i.e., spaced 120 degrees apart along the circumferenceof a circle s which is generally concentric with the circular firstpatterned electrode 12 b and has a radius r, as viewed in plan (FIG. 5).

On the lower surface of the wiring board 11 b are formed a power supplywiring pattern 15 b electrically connected to the first patternedelectrode 12 b via a through hole 17 b, a power supply wiring pattern 16b electrically connected to the second patterned electrode 13 b via athrough hole 18 b, a power supply wiring pattern 16 b′ electricallyconnected to the second patterned electrode 13 b′ via a through hole 18b′, and a power supply wiring pattern 16 b″ electrically connected tothe second patterned electrode 13 b″ via a through hole 18 b″.

The LED chip 19 b for emitting red light, the LED chip 19 b′ foremitting green light, and the LED chip 19 b″ for emitting blue light aremounted on the second wiring patterns 13 b, 13 b′ and 13 b″,respectively, by die bonding. The LED chips 19 b, 19 b′ and 19 b′ areelectrically connected to the first patterned electrode 12 b by wirebonding using thin metal wires 20 b, 20 b′ and 20 b″, respectively.

The metal wires 20 b, 20 b′ and 20 b″ are so arranged as to extendradially outward as viewed in plan (FIG. 5).

Subsequently, similarly to the first and the second embodiments, anappropriate amount of transparent synthetic resin in a liquid state isdropped onto the upper surface of the wiring board 11 b at the portionformed with the first patterned electrode 12 b (preferably at thegeneral center of the first patterned electrode 12 b) to cause the resinto bulge into a hemispherical configuration, and then the bulged resinis hardened. As a result, a hemispherical lens member 21 b is providedwhich packages the LED chips 19 b, 19 b′, 19 b″ and the metal wires 20b, 20 b′, 20 b′.

As noted above, the metal wires 20 b, 20 b′, 20 b″ for the LED chips 19b, 19 b′, 19 b″ extend radially outward. Therefore, the radially outwardflow of the liquid transparent synthetic resin dropped onto the firstpatterned electrode 12 b occurs generally in the same manner atrespective portions provided with the metal wires 20 b, 20 b′, 20 b′. Asa result, the liquid transparent synthetic resin reliably spreads tobecome a round circle, as viewed in plan (FIG. 5).

In the third embodiment again, the peripheral edge of the cutout 14 b ofthe first patterned electrode 12 b includes indentations 12 b′ enteringbetween the second patterned electrodes 13 b, 13 b′, 13 b″. Theprovision of the indentations 12 b′ increases the light reflectivesurface comprising the first patterned electrode 12 b by as much as theportions entering between the second patterned electrodes 13 b, 13 b′and 13 b″.

FIGS. 7, 8 and 9 show a fourth embodiment.

In the fourth embodiment, a number of light emitting devices 22according to the third embodiment are arranged in a matrix of rows andcolumns on a single common wiring board 23, thereby providing a panelfor displaying letters or images in full color utilizing three primarycolors of light.

In the fourth embodiment, a conductor pattern 24 is formed on the entireupper surface of the common wiring board 23 except the portions formedwith the first circular patterned electrodes 12 b, with a ring-like gap25 formed between the conductor pattern 24 and each of the firstpatterned electrodes 12 b. The conductor pattern 24 is electricallyconnected to the first patterned electrode 12 b of each light emittingdevice 22 via a power supply wiring pattern 26 formed on the lowersurface of the common wiring board 23 and through holes 27, 28, 29.

As indicated by double-dashed lines, the obverse surface of theconductor pattern 24 is covered with an insulating film 30.

With such a structure again, the above-described advantages can beobtained, because the ring-like gap 25 is provided between the firstpatterned electrode 12 b of each light emitting device 22 and theconductor pattern 24 and the first patterned electrode 12 b is in theform of a complete circle. The power supply for the first patternedelectrode 12 b of each light emitting device 22 can be performed by theconductor pattern 24 formed on the upper surface of the common wiringboard 23. Accordingly, the structure of the power supply wiring patternfor the light emitting device 22 can be simplified. Further, theentirety of the conductor pattern 24 can be advantageously utilized as alight reflective surface.

1. A light emitting device comprising: a first patterned electrode and asecond patterned electrode both of which made of a metal film andprovided on an obverse surface of a wiring board; an LED chip mounted onthe second patterned electrode; a metal wire electrically connecting theLED chip and the first patterned electrode to each other; and a lensmember made of a transparent synthetic resin and provided on the obversesurface of the wiring board for packaging the LED chip and the metalwire; wherein the first patterned electrode is circular and has acentral cutout, the second patterned electrode being arranged in thecutout.
 2. A light emitting device comprising: a first patternedelectrode and a plurality of second patterned electrodes, the first andsecond patterned electrodes being made of a metal film and provided onan obverse surface of a wiring board; LED chips each mounted on arespective one of the second patterned electrodes; metal wires eachelectrically connecting a respective one of the LED chips and the firstpatterned electrode; and a lens member made of a transparent syntheticresin and provided on the obverse surface of the wiring board forpackaging the LED chips and the metal wires; wherein the first patternedelectrode is circular and has a central cutout, the second patternedelectrodes are arranged in the cutout while being equally spaced fromeach other along a circumference of a circle which is generallyconcentric with the circle of the first patterned electrode, and whereinthe metal wires electrically connecting the LED chips mounted on thesecond patterned electrodes to the first patterned electrode extendradially outward.
 3. The light emitting device according to claim 1,wherein the wiring board has a reverse surface formed with a powersupply wiring pattern for electrical connection to the first patternedelectrode and the second patterned electrode via a through-hole formedin the wiring board.
 4. The light emitting device according to claim 2,wherein the cutout of the first patterned electrode has a peripheraledge which includes an indentation entering between the second patternedelectrodes.
 5. A method of making a light emitting device, comprisingthe steps of: forming, on a wiring board, a first patterned electrode ofa metal film into a circular configuration while forming a cutout at acenter of the first patterned electrode; forming a second patternedelectrode of a metal film in the cutout; mounting an LED chip on thesecond patterned electrode; electrically connecting the LED chip and thefirst patterned electrode to each other via a metal wire; and forming alens member by dropping transparent synthetic resin in a liquid stateonto the first patterned electrode so that the transparent syntheticresin bulges to cover the LED chip and the metal wire and then hardeningthe synthetic resin.
 6. The light emitting device according to claim 2,wherein the wiring board has a reverse surface formed with a powersupply wiring pattern for electrical connection to the first patternedelectrode and the second patterned electrode via a through-hole formedin the wiring board.